1. Field of the Invention
The present invention relates to a fertilizer material for soils and, more particularly, to an acidulated slag fertilizer.
2. Description of the Prior Art
Highly acidic fertilizers for soils made from iron and copper refining slags are already well known. However, there has been a continuing need to develop fertilizers, and processes for making same, which have increased acidity and which will release their acidity to the soil over an extended period of time.
Processes for making acidic fertilizers from reverberatory copper refining slag by treatment thereof with acid are taught in my earlier U.S. Pat. Nos. 2,927,851 and 3,145,093. In the former patent, the slag is treated with concentrated sulfuric acid in the presence of relatively large quantities of water. In the latter patent, dry (non-wetted) slag is treated with hot, dilute aqueous solutions of sulfuric acid. In both processes, the reaction between the water present, the acid and the slag is virtually instantaneous and only partial chemical decomposition of the oxidic-silicic components of the slag takes place with the result that the products still contain substantial amounts of acid reactable, but unreacted, residues.
My U.S. Pat. No. 3,201,222 relates to a product suitable for the treatment of both alkaline and acid soils. The product may be formed by reacting slag materials such as that obtained from the process of refining copper in a reverberatory furnace with a suitable amount of concentrated orthophosphoric acid, without the separate addition of any extra water, and by thereafter maintaining the product resulting from the slag-acid reaction at an elevated temperature for a time interval sufficient to permit all of the iron values originally present in the slag, both as metallic iron and as various iron oxides, to be converted to iron salts of orthophosphoric acid.
In my U.S. Pat. No. 3,418,238, I describe a process for the preparation of a modified silica gel derived from mineral acid extracts of waste slag resulting from the reverberatory refining of copper pyritic type ores which comprises treating the slag with an aqueous solution of at least one mineral acid to dissolve the acid-soluble portion of the slag under conditions whereby the temperature of the slag-acid system does not generally exceed 175.degree. F. so that the formation of a silica gel is avoided, separating the resulting mineral acid solution from the solid and insoluble residue, modifying the silicic acid dihydrate containing solution by the addition of chemicals to be carried by the silica and altering the hydrogen ion concentration of the silicic acid dihydrate by driving off water so as to convert the silicic acid dihydrate to silicic acid monohydrate at which point the system gels to provide a modified silica gel which acts as a carrier for the added chemicals.
Soil fertilizing and soil improving gel products are disclosed in my U.S. Pat. No. 3,860,409. The products may be made by a process which comprises admixing a pulverized waste copper slag with concentrated sulfuric acid having a strength of from 95 to 98% by weight and adding limited quantities of water to the acid wetted slag whereby the resulting slag-acid-water composition reacts to form a dry granular aggregate composed of about 80-85% water soluble partially hydrated, but mostly anhydrous, metallic sulfate salts in combination with metasilicic acid-adsorbed sulfuric acid, about 15-20% sulfuric acid insoluble metal silicates, and approximately 1-2% of elemental sulfur.